Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information,
see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module,
and to see a list of the releases in which each feature is supported, see the feature information table.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature
Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Information About ISATAP Tunnel Support for IPv6

Overlay Tunnels for IPv6

Overlay tunneling encapsulates IPv6 packets in IPv4 packets for delivery across an IPv4 infrastructure (a core network or
the figure below). By using overlay tunnels, you can communicate with isolated IPv6 networks without upgrading the IPv4 infrastructure
between them. Overlay tunnels can be configured between border devices or between a border device and a host; however, both
tunnel endpoints must support both the IPv4 and IPv6 protocol stacks. IPv6 supports the following types of overlay tunneling
mechanisms:

Manual

Generic routing encapsulation (GRE)

IPv4-compatible

6to4

Intrasite Automatic Tunnel Addressing Protocol (ISATAP)

Figure 1. Overlay Tunnels

Note

Overlay tunnels reduce the maximum transmission unit (MTU) of an interface by 20 octets (assuming that the basic IPv4 packet
header does not contain optional fields). A network that uses overlay tunnels is difficult to troubleshoot. Therefore, overlay
tunnels that connect isolated IPv6 networks should not be considered a final IPv6 network architecture. The use of overlay
tunnels should be considered as a transition technique toward a network that supports both the IPv4 and IPv6 protocol stacks
or just the IPv6 protocol stack.

Use the table below to help you determine which type of tunnel that you want to configure to carry IPv6 packets over an IPv4
network.

Simple point-to-point tunnels that can be used within a site or between sites.

Can carry IPv6 packets only.

GRE- and IPv4- compatible

Simple point-to-point tunnels that can be used within a site or between sites.

Can carry IPv6, Connectionless Network Service (CLNS), and many other types of packets.

IPv4- compatible

Point-to-multipoint tunnels.

Uses the ::/96 prefix. We do not recommend using this tunnel type.

6to4

Point-to-multipoint tunnels that can be used to connect isolated IPv6 sites.

Sites use addresses from the 2002::/16 prefix.

6RD

IPv6 service is provided to customers over an IPv4 network by using encapsulation of IPv6 in IPv4.

Prefixes can be from the SP’s own address block.

ISATAP

Point-to-multipoint tunnels that can be used to connect systems within a site.

Sites can use any IPv6 unicast addresses.

Individual tunnel types are discussed in detail in this document. We recommend that you review and understand the information
about the specific tunnel type that you want to implement. When you are familiar with the type of tunnel you need, see the
table below for a summary of the tunnel configuration parameters that you may find useful.

Table 2. Tunnel Configuration Parameters by Tunneling Type

Tunneling Type

Tunnel Configuration Parameter

Tunnel Mode

Tunnel Source

Tunnel Destination

Interface Prefix or Address

Manual

ipv6ip

An IPv4 address, or a reference to an interface on which IPv4 is configured.

An IPv4 address.

An IPv6 address.

GRE/IPv4

gre ip

An IPv4 address.

An IPv6 address.

IPv4- compatible

ipv6ip auto-tunnel

Not required. These are all point-to-multipoint tunneling types. The IPv4 destination address is calculated, on a per-packet
basis, from the IPv6 destination.

Not required. The interface address is generated as ::tunnel-source/96.

6to4

ipv6ip 6to4

An IPv6 address. The prefix must embed the tunnel source IPv4 address.

6RD

ipv6ip 6rd

An IPv6 address.

ISATAP

ipv6ip isatap

An IPv6 prefix in modified eui-64 format. The IPv6 address is generated from the prefix and the tunnel source IPv4 address.

ISATAP Tunnels

ISATAP is an automatic overlay tunneling mechanism that uses the underlying IPv4 network as a NBMA link layer for IPv6. ISATAP
is designed for transporting IPv6 packets
within a site where a native IPv6 infrastructure is not yet available; for example, when sparse IPv6 hosts are deployed for testing.
ISATAP tunnels allow individual IPv4 or IPv6 dual-stack hosts within a site to communicate with other such hosts on the same
virtual link, basically creating an IPv6 network using the IPv4 infrastructure.

The ISATAP router provides standard router advertisement network configuration support for the ISATAP site. This feature
allows clients to automatically configure themselves as they would do if they were connected to a GigabitEthernet or FastEthernet.
It can also be configured to provide connectivity out of the site. ISATAP uses a well-defined IPv6 address format composed
of any unicast IPv6 prefix (/64), which can be link local, or global (including 6to4 prefixes), enabling IPv6 routing locally
or on the Internet. The IPv4 address is encoded in the last 32 bits of the IPv6 address, enabling automatic IPv6-in-IPv4 tunneling.

Although the ISATAP tunneling mechanism is similar to other automatic tunneling mechanisms, such as IPv6 6to4 tunneling,
ISATAP is designed for transporting IPv6 packets
within a site, not
between sites.

ISATAP uses unicast addresses that include a 64-bit IPv6 prefix and a 64-bit interface identifier. The interface identifier
is created in modified EUI-64 format in which the first 32 bits contain the value 000:5EFE to indicate that the address is
an IPv6 ISATAP address. The table below describes an ISATAP address format.

Table 3. IPv6 ISATAP Address Format

64 Bits

32 Bits

32 Bits

link local or global IPv6 unicast prefix

0000:5EFE

IPv4 address of the ISATAP link

As shown in the table above, an ISATAP address consists of an IPv6 prefix and the ISATAP interface identifier. This interface
identifier includes the IPv4 address of the underlying IPv4 link. The following example shows what an actual ISATAP address
would look like if the prefix is 2001:DB8:1234:5678::/64 and the embedded IPv4 address is 10.173.129.8. In the ISATAP address,
the IPv4 address is expressed in hexadecimal as 0AAD:8108:

2001:DB8:1234:5678:0000:5EFE:0AAD:8108

How to Configure ISATAP Tunnel Support for IPv6

Configuring ISATAP Tunnels

Before you begin

The tunnel source command used in the configuration of an ISATAP tunnel must point to an interface with an IPv4 address configured. The ISATAP
IPv6 address and prefix (or prefixes) advertised are configured as for a native IPv6 interface. The IPv6 tunnel interface
must be configured with a modified EUI-64 address because the last 32 bits in the interface identifier are constructed using
the IPv4 tunnel source address.

Configuration Examples for ISATAP Tunnel Support for IPv6

Example: Configuring ISATAP Tunnels

The following example shows the tunnel source defined on GigabitEthernet 0/0/0 and thetunnel mode command used to configure the ISATAP tunnel. Router advertisements are enabled to allow client autoconfiguration.

Standards and RFCs

Standard/RFC

Title

RFCs for IPv6

IPv6 RFCs

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use
these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products
and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

Feature Information for ISATAP Tunnel Support for IPv6

The following table provides release information about the feature or features described in this module. This table lists
only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise,
subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco
Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 4. Feature Information for ISATAP Tunnel Support for IPv6

Feature Name

Releases

Feature Information

ISATAP Tunnel Support for IPv6

Cisco IOS XE Release 2.1

ISATAP is an automatic overlay tunneling mechanism that uses the underlying IPv4 network as a NBMA link layer for IPv6.